Mobile systems have been developed due to the need to free people to move away from fixed telephone terminals without making it more difficult to reach them. While the use of different data transmission services in offices has increased, different data services have also been introduced into mobile systems. Portable computers enable efficient data processing anywhere a user happens to be. Mobile networks provide a user with an effective access network to the actual data networks for the purpose of mobile data transmission. Therefore, different new forms of data services are designed for present and future mobile networks. Mobile data transmission is particularly well supported by digital mobile systems, such as the Pan-European mobile system GSM (Global System for Mobile Communication).
General packet radio service (GPRS) is a new service in the GSM system and it is one of the subjects of the GSM standardization of phase 2+ in the ETSI (European Telecommunication Standard Institute). The GPRS operational environment consists of one or several subnetwork service areas that are interconnected by a GPRS backbone network. The subnetwork comprises a number of packet data service nodes (SN) that are referred to as servicing GPRS support nodes (SGSN) herein. Each SGSN is connected to the GSM mobile network (typically to base station systems) in such a way that it is capable of providing mobile data terminals with the packet data service via several base stations, i.e. cells. The intermediate mobile network provides packet switched data transmission between a support node and mobile data terminals. The different subnetworks are connected to an external data network, for example a packet switched public data network PSPDN, via special GPRS gateway support nodes GGSN. Therefore, packet data transmission is provided between mobile data terminals and external data networks by means of the GPRS, and the GSM network operates as an access network.
In such a GPRS network, a mobile station MS (a packet radio terminal equipment) may have different operating states: an idle state, a standby state and an active state.
In the idle state, the MS is inaccessible to the GPRS network, which does not maintain any dynamic data about the current state or location of the MS. The MS does not perform reception or transmission of data packets, either. If the MS is double-acting, i.e. it is capable of operating both in the GPRS and the GSM networks, it may be located in the GSM network while operating in the GPRS idle state. The MS may change from the idle state to the standby state by logging on to the GPRS network.
In the standby state, the MS has logged on to the GPRS network. In the GPRS network, dynamic routing and GPRS contexts have been formed for the MS. The MS and the GPRS network communicate mainly through signalling. The MS performs the selection of the GPRS routing area (RA) and the GPRS cell (cell identity, physical channel) locally. The MS informs the GPRS network when it arrives at a new RA (a few or a few dozens of cells), but it does not inform the GPRS network of a change in the GPRS channel (cell identity, physical channel). Therefore, the GPRS only knows the RA of the MS when the MS is in the standby state. The MS changes from the standby state to the active state either when the GPRS network pages the MS in the RA or when the MS starts transmitting data. The MS changes from the standby state to the idle state either when it logs out of the GPRS network or when the standby timer expires. The standby timer is used to control the time the MS remains in the standby state. The standby timer is reset and started every time the MS changes to the standby state (either from the idle or the active state).
In the active state, the GPRS network also knows the GPRS channel the MS has selected, in addition to the RA of the MS. The MS updates its new GPRS channel to the GPRS network when the channel is changed as a result of local cell (re)selection. The MS transmits and receives data packets in this state. The MS may remain in the active state even when no data is transmitted. In the downlink direction (from the network to the MS), the MS may receive either continuously (CRX) or discontinuously (DRX). The active timer is used to control the time the MS remains in the active state after a data packet has been successfully moved between the MS and the GPRS network. The MS changes from the active state to the standby state when the active timer expires. In order to change from the active state to the idle state, the MS starts the logoff out of the network.
The standby timer and the active timer are maintained both in the MS and in the GPRS network to control the time the MS stays in the standby state or in the active state, respectively. These timers are usually set for the same period of time both in the MS and in the GPRS network. Normally the timers have a certain default value that the GPRS network may change dynamically by transmitting a new value to the MS. If the new value is zero, it immediately forces the MS to enter from the active state to the standby state or, correspondingly, from the standby state to the idle state. The MS may also ask the GPRS network to lengthen the time of the timer and the GPRS network may either accept or reject this request.
The aim is to minimize, by means of these different states, the loading caused by the less active mobile stations on the GPRS network, but on the other hand, to maintain the network throughput and speed as good as possible for data transmission. Further, the different states can be used to decrease the power consumption of the MSs.
For example in the active state, the MS updates its location in connection with each cell crossover (handover), which means an increased signalling load and power consumption of the MS. Therefore, it is preferable to make an MS that does not actively transmit data packets to change to the standby state, as it is currently performed with the active timer. In the standby state, the MS updates its location only when it changes the RA, which means a lower signalling load and power consumption. In the standby state, the MS may also use discontinuous reception DRX, which further decreases the consumption of power. On the other hand, data transmission to an MS first requires that the MS is paged, which slows down the start-up of data transmission. In the idle state there is no regular signalling.
The problem detected by the Applicant is related to the fact that controlling operating states of an MS with timers is not an optimal solution, but there is still rather a lot of unnecessary signalling and resulting power consumption of an MS in the GPRS network. For example, the time of the active timer could be typically one minute or a few minutes. After it has transmitted the last data packet, the MS is in the active state for the aforementioned time even if it had no more data to transmit or receive. During this period, in the worst case there may still be several cell crossovers before the active timer expires, thus moving the MS to the standby state. Assume, for example, that a packet radio system is used for collecting a road toll. When a car has passed the toll booth and paid the toll via the GPRS system, it can pass several base stations before the active timer expires.
Another problem is related to a situation where an MS wants to stay in the active state in order to maintain a high quality of service (QoS) in case it might transmit or receive data in the near future. For this purpose, the MS may request for an extension of the time of the active timer. If the GPRS network rejects the request, the MS is forced to change to the standby state against its will.